The present invention relates to a system for automatically correcting the position of the slide in a press, and more particularly to a system for automatically adjusting the up-down relative position relationship between the slide and the bolster so that the relative distance between the bolster and the slide at the bottom dead center will be in a predetermined range.
In some kinds of press work, for example in coining operation, problems could arise from the degree of accuracy of the position of the bottom dead center, i.e. variations in the relative distance between the bolster and the slide at the bottom dead center. Such variations in the relative distance include the variation from stroke to stroke, the variation dependent on the number of successive strokes (spm), and the variation due to the thermal expansion of press components resulting from the heat of friction involved in the drive assembly of the slide. Of these variations, the stroke-to-stroke variation can be diminished sufficiently by designing and building the press with improved precision, but difficulties still remain to be eliminated in reducing the variation due to the succession of strokes or to heat to a small value, for example, of up to 10 .mu.m. Accordingly it is usual practice to circulate a large quantity of oil through the press to prevent the rise of temperature, but this requires much power for the circulation of oil and temperature control and is therefore not economical. Further when the press is held out of operation and is brought into operation again, it is likely that the bottom dead center will not be accurately positioned. For example, the operation of the press is interrupted for the replacement or supply of die, coil material, or recoil material of worked product, and the temperature of the drive assembly for the slide gradually falls during the interruption, gradually altering the position of the top dead center of the slide. This gradually alters the up-down relative position relationship between the slide and the bolster. Consequently, if the press in this state is brought into operation again, it is likely that the relative distance between the bolster and the slide at the top dead center will be outside a predetermined range.